TITLE: GCN CIRCULAR NUMBER: 42716 SUBJECT: EP251023a: ISON/UAFO and AbAO optical observations DATE: 25/11/17 12:54:12 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), A. Pozanenko (IKI), A. Kochergin (UAFO), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN: We observed the field of the EP transient EP251023a (Wu et al., GCN 42388) with the RC-500 (0.5m) telescope of UAFO/ISON-Ussuriysk observatory on Oct., 23, 2025 starting at (UT) 17:51:51, and the AS-32 0.7m telescope of the Abastumani Observatory (AbAO) on Oct., 24, 2025, starting at (UT) 22:53:36. Several 60-second exposures in R-filter were obtained during each observational epoch. The optical counterpart (Wortley et al., GCN 42387; Li et al., GCN 42389; Liu et al., GCN 42391; Mandarakas et al., GCN 42400; Lipunov et al., GCN 42405; Selezneva et al., GCN 42406; Mohan et al., GCN 42411; Rakotondrainibe et al., GCN 42420; Rajabov et al., GCN 42422; Volnova et al., GCN 42468) is clearly detected in the stacked UAFO image and is not detected in that of the AbAO. The preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Tel. (mid,days) (n*s) (3sigma) 2025-10-23 17:51:51 0.67889 100*60 R 19.97 0.22 20.9 UAFO/RC-500 2025-10-24 22:53:36 1.88138 40*60 R n/d n/d 20.5 AbAO/AS-32 The photometry is based on several nearby PS1 stars (Lupton's R-band transformation, Vega system) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42716. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...